According to the National Building Code of Canada (NBC) 2020 and good construction practice, when can horizontal soffit forms and shores be removed from a suspended concrete slab that is designed to carry full service loads?

Question: According to the National Building Code of Canada (NBC) 2020 and good construction practice, when can horizontal soffit forms and shores be removed from a suspended concrete slab that is designed to carry full service loads?

Answer options:

• After 3 days, regardless of temperature.
• Once the concrete has achieved 50% of its specified compressive strength. ✅ Only after the concrete has achieved its specified compressive strength and passes a structural engineer's inspection, typically requiring 70-85% of f'c for partially de-shored systems or 100% for full de-shoring.
• When the concrete appears dry to the touch.

Correct answer: Only after the concrete has achieved its specified compressive strength and passes a structural engineer's inspection, typically requiring 70-85% of f'c for partially de-shored systems or 100% for full de-shoring.

Explanation: The removal of horizontal soffit forms and shores is a critical structural decision. It should only occur after the concrete has gained sufficient strength, typically a significant percentage (e.g., 70-85% for re-shoring, or 100% for full removal) of its specified design strength (f'c), and is always subject to a structural engineer's approval based on site-specific testing and evaluation to ensure safety and prevent structural damage.